package thinkingInJava.String_.regex_;
// page 567 对映射文件部分加锁
//: io/LockingMappedFiles.java
//Locking portions of a mapped file.
//{RunByHand}
import java.nio.*;
import java.nio.channels.*;
import java.io.*;

public class LockingMappedFiles {
	static final int LENGTH = 0x8FFFFFF; // 128 MB
	static FileChannel fc;
	public static void main(String[] args) throws Exception {
		fc =
				new RandomAccessFile("thinkingInJava.dat", "rw").getChannel();
		MappedByteBuffer out =
				fc.map(FileChannel.MapMode.READ_WRITE, 0, LENGTH);
		for(int i = 0; i < LENGTH; i++)
			out.put((byte)'x');
		new LockAndModify(out, 0, 0 + LENGTH/3);
		new LockAndModify(out, LENGTH/2, LENGTH/2 + LENGTH/4);
	}
	private static class LockAndModify extends Thread {
		private ByteBuffer buff;
		private int start, end;
		LockAndModify(ByteBuffer mbb, int start, int end) {
			this.start = start;
			this.end = end;
			mbb.limit(end);
			mbb.position(start);
			buff = mbb.slice();
			start();
		}
		public void run() {
			try {
				// Exclusive lock with no overlap: 
				FileLock fl = fc.lock(start, end, false); // 只能得到通道上的锁,而不是 Buffer 的锁
				System.out.println("Locked: "+ start +" to "+ end);
				// Perform modification:
				while(buff.position() < buff.limit() - 1)
					buff.put((byte)(buff.get() + 1));
				fl.release();
				System.out.println("Released: "+start+" to "+ end);
			} catch(IOException e) {
				throw new RuntimeException(e);
			}
		}
	}
} ///:~
